1. Technical Field
The present disclosure is directed to communications connectors and, more particularly, to connection systems equipped and configured to address and/or compensate for electrical noise or crosstalk (e.g., near-end crosstalk or NEXT).
2. Background Art
Devices for interfacing with high frequency data transfer media are generally known. Modular jack housing inserts have been developed that facilitate interface with connectors, i.e., plugs, that in turn interact with unshielded twisted pair (UTP) media. UTP media finds widespread application in structured cabling applications, e.g., in local area network (LAN) implementations and other in-building voice and data communications applications. In a UTP cable, a plurality of twisted copper pairs are twisted together and wrapped with a plastic coating. Individual wires generally have a diameter of 0.4-0.8 mm. Twisting of the wires increases the noise immunity and reduces the bit error rate (BER) associated with data transmission thereover. Also, using two wires rather than one to carry each signal permits differential signaling to be used, which offers enhanced immunity to the effects of external electrical noise.
As an alternative to UTP media, shielded twisted pair (STP) media is used in certain structured cabling applications. STP media includes shielding, e.g., a foil or braided metallic covering, that generally reduces the effects of outside interference. However, as compared to STP media, UTP media offers reduced cost, size and cable/connector installation time. In addition, the use of UTP media, as opposed to STP media, eliminates the possibility of ground loops (i.e., current flowing in the shield because the ground voltage at each end of the cable is not exactly the same, thereby potentially inducing interference into the cable that the shield was intended to protect). In short, UTP media is a flexible, low cost media having widespread application in voice and/or data communications.
The wide acceptance and use of UTP for data and voice transmission is also driven by the large installed base, low cost and ease of new installations. Another important feature of UTP is that it can be used for varied applications, such as for Ethernet, Token Ring, FDDI, ATM, EIA-232, ISDN, analog telephone (POTS), and other types of communication. This enables the same type of cable and system components (such as jacks, plugs, cross-patch panels and patch cables) to be used for an entire building installation, unlike STP media.
UTP media is being used for systems having increasingly higher data rates. In data transmission, the signal originally transmitted through the data transfer media is not necessarily the signal received. The received signal will consist of the original signal as modified by various distortions and additional unwanted signals introduced over the transmission path. Such distortions and unwanted signals affect the original signal between transmission and reception and are commonly collectively referred to as “electrical noise” or simply “noise.” Noise can be a primary limiting factor in the performance of a communication system. Indeed, many problems may arise from the existence and/or introduction of noise during data transmission, such as data errors, system malfunctions and loss of the original signals (in whole or in part).
The transmission of data by itself causes unwanted noise. Electromagnetic energy, induced by the electrical energy in the individual signal carrying lines within the data transfer media and data transfer connecting devices, radiates onto adjacent lines in the same media or device. This cross coupling of electromagnetic energy (i.e., electromagnetic interference or EMI) from a “source” line to a “victim” line is called crosstalk. Most data transfer media consist of multiple pairs of lines bundled together. Communication systems typically incorporate many such media and connectors for data transfer. Thus, there exists an opportunity for significant crosstalk interference.
Electromagnetic energy waves can be derived by Maxwell's wave equations. These equations are basically defined using electric and magnetic fields. In unbounded free space, a sinusoidal disturbance propagates as a transverse electromagnetic wave. This means that the electric field vectors are perpendicular to the magnetic field vectors lying in a plane perpendicular to the direction of the wave. Crosstalk results in a waveform shaped differently than the one originally transmitted.
Crosstalk can be categorized in one of two forms. Near end crosstalk, commonly referred to as NEXT, arises from the effects of near field capacitive (electrostatic) and inductive (magnetic) coupling between source and victim electrical transmissions. NEXT increases the additive noise at the receiver and therefore degrades the signal to noise ratio (SNR). NEXT may be the most significant impediment to effective data transfer because the high-energy signal from an adjacent line can induce relatively significant crosstalk into the primary signal. A second form of crosstalk is far end crosstalk (FEXT) which arises due to capacitive and inductive coupling between the source and victim electrical devices at the far end or opposite end of the transmission path. FEXT is typically less of an issue because the far end interfering signal is attenuated as it traverses the loop.
Another major source of distortion for high speed signal transmission may be mismatch of transmission impedances. As the signal travels along transmission media, various interconnections are generally encountered. Each interconnection has its own internal impedance relative to the traveling signal. For UTP cabling, the transmission media impedance is generally 100 Ohms. Any offsets or differences in impedance values from connecting devices will produce signal reflections. Generally, signal reflections reduce the amount of transmitted signal energy to the receiver and/or distort the transmitted signal. Thus, signal reflections can lead to an undesirable increase data loss.
To accommodate higher frequency data communications, commercially available connection systems generally include compensation functionality that is intended to compensate for electrical noise, e.g., noise/crosstalk introduced in the connection assembly or assemblies. Since demands on networks using UTP systems (e.g., 100 Mbit/s, 1200 Mbit/s transmission rates and higher) have increased, it has become necessary to develop industry standards for higher system bandwidth performance. What began as simple analog telephone service and low speed network systems, has now become high speed data systems. As the speeds have increased, so has the noise.
The ANSI/TIA/EIA 568B standard defines electrical performance for systems that operate in the 1-250 MHz frequency bandwidth range. Exemplary data systems that utilize the 1-250 MHz frequency bandwidth ranges are IEEE Token Ring, Ethernet10Base-T and 100Base-T systems. Five performance categories have been defined by ANSI/TIA/EIA-568.2-10 and the subsequent ANSI/TIA/EIA-568B.2 promulgations, as shown in the Table 1 below. Compliance with these performance standards are used, inter alia, to identify cable/connector quality.
TABLE 1Characteristic Specified upCategoryto Frequency (MHz)Exemplary Uses5100TP-PMD, SONet, OC-3(ATM), 100BASE-TX.5e10010-100BASE-T.6250100-1000BASE-T.6A5001000-10GBASE-T.
UTP cable standards are also specified in the EIA/TIA-568 Commercial Building Telecommunications Wiring Standard, and such standards include electrical and physical requirements for UTP, STP, coaxial cables and optical fiber cables. For UTP, the requirements include (i) four individually twisted pairs per cable, (ii) each pair has a characteristic impedance of 100 Ohms +/−15% (when measured at frequencies of 1 to 100 MHz); and (iii) 24 gauge (0.5106-mm-diameter) or optionally 22 gauge (0.6438 mm diameter) copper conductors are specified. Additionally, the ANSI/TIA/EIA-568 standard specifies the color coding, cable diameter and other electrical characteristics, such as the maximum cross-talk (i.e., how much a signal in one pair interferes with the signal in another pair—through capacitive, inductive and other types of coupling).
The Category 5 cabling systems provided sufficient NEXT margins to allow for the high NEXT that occurs when using the present UTP system components. However, the demand for higher frequencies, more bandwidth and improved system performance (e.g., Ethernet 1000Base-T) for UTP cabling systems required enhanced system design/performance. More particularly, the TIA/EIA Category 6 standard extended performance requirements to frequency bandwidths of 1 to 250 MHz, requiring minimum NEXT values at 100 MHz to be −39.9 dB and −33.1 dB at 250 MHz for a channel link, and minimum NEXT values at 100 MHz to be −54 dB and 46 dB at 250 MHz for connecting hardware. The increased bandwidth accommodated by the Category 6 standard required increased focus on noise compensation.
More recently, the TIA/EIA 568 Category 6A or EIA568B.2-10 Augmented Category 6 cabling standard extends performance requirements to still higher frequencies, i.e., frequency bandwidths of 1 to 500 MHz. More particularly, the addendum specifies (i) minimum NEXT values at 100 MHz to be −39.9 dB and −26.1 dB at 500 MHz for a channel link, and (ii) minimum NEXT values at 100 MHz to be −54 dB and −34 dB at 500 MHz for connecting hardware. The requirements for Return Loss for a channel are −12 dB at 100 MHz and −6 dB at 500 MHz, and for a connector the corresponding requirements are −28 dB at 100 MHz and −14 dB at 500 MHz.
As noted above, a key element for compensation of NEXT and FEXT is the design and operation of the electrical interface, e.g., the electrical communication between jack and plug connectors. The standard modular jack housing is configured and dimensioned in compliance with the FCC part 68.500 standard which provides compatibility and matability between various media manufacturers. The standard FCC part 68.500 style for modular jack housing which does not add compensation methods/functionality to reduce crosstalk. This standard modular jack housing provides a straightforward approach/design and, by alignment of lead frames in a parallel, uniform pattern, high NEXT and FEXT are generally produced for certain adjacent wire pairs. More particularly, the standard FCC part 68.500 modular jack housing connector defines two lead frame section areas. Section one defines a matable area for electrical plug contact and section two is the output area of the modular jack housing. Section one aligns the lead frames in a parallel, uniform pattern from lead frame tip to the bend location that enters section two, thus producing relatively high NEXT and FEXT noises. Section two also aligns the lead frames in a parallel, uniform pattern from lead frame bend location to lead frame output, thus producing/allowing relatively high NEXT and FEXT noises.
There have been efforts aimed at reducing crosstalk through modified housing designs. For example, U.S. Pat. No. 7,281,957 to Caveney et al. discloses a communication connector with a flexible circuit board. The connector utilizes a flexible circuit board that is electrically and mechanically connected to the plug interface pins. The flexible circuit board makes electrical contact in two locations, one at the connectors plug interface pin section, and also at the insulation displacement contact IDC section. The flexible circuit board is used to transport the electrical signals from input plug/pin interface to IDC or visa versa. By design, this connector reduces noise but at the expense of excessive pin lengths that can increase or enhance unwanted noises. Another potential issue with respect to the connector of the Caveney '957 patent could be the insertion of an FCC regulated RJ11 plug insertion into the plug/pin interface. Because of the deep depression of force that is applied to the outer pins, potential damage could occur to the flexible circuit board, potentially rendering the connector virtually unusable. This method could be effective at reducing crosstalk, but potentially at a substantial cost (e.g., due to the usage and size of the flexible circuit board).
A similar approach to crosstalk reduction is disclosed in U.S. Pat. No. 7,309,261 Caveney et al. The Caveney '261 patent describes a communication connector that utilizes a flexible circuit board that makes electrical connection to the plug interface pins. In one instance, the electrical connections are physically and permanently connected to the plug interface pins by various welding methods. In another instance, the electrical connections are plug interface pins that make electrical connections to a rigid and stationary printed circuit board. Although the connector of the Caveney '261 patent has the potential to reduce crosstalk, the methods disclosed could potentially increase fabrication costs and introduce mechanical complication. Permanently attached printed circuit boards, whether flexible or rigid, have the potential to break electrical connection or produce open circuit data connections if a FCC part 47 out of specification plug Register Jack RJ45 is inserted. The usage of an electrical connection to a stationary printed circuit board further places the compensation at a distance that is further away from origination noise source, thus increasing the chances of allowing additional unwanted noise to be injected into adjacent pairs.
U.S. Pat. No. 6,139,371 to Troutman et al. discloses a communication connector assembly having a base support and first and second pairs of terminal contact wires with base portions mounted on the base support. The free end portions of the contact wires define a zone of contact within which electrical connections are established with a mating connector, and each pair of contact wires defines a different signal path in the connector assembly. The first and the second pair of contact wires have corresponding leading portions extending from the free end portions to a side of the zone of contact opposite from the base portions. A leading portion of a contact wire of the first pair and a leading portion of a contact wire of the second pair are constructed and arranged for capacitively coupling to one another, thus conveying capacitive crosstalk compensation to the zone of contact where offending crosstalk is introduced by a mated connector. The additional coupling of the connector assembly of the Troutman '371 patent may be inadequate in reducing crosstalk to a required degree because, inter alia, the elongated plates are crossed/overlapped and also adjacent, thus creating unwanted parallelisms between contacts 3 to 4 and contacts 5 to 6 and undesirably increasing crosstalk noises. Although crosstalk noise may be reduced by the design of the connector assembly of the Troutman '371 patent, the effective complex modes of coupling may be more than doubled, which potentially increases NEXT, FEXT and noise variation factors.
U.S. Pat. No. 6,176,742 to Arnett et al. discloses an electrical connector that provides capacitive crosstalk compensation coupling in a communication connector by the use of a capacitor compensation assembly. One or more crosstalk compensation capacitors are supported in the housing. Each compensation capacitor includes a first electrode having a first terminal, a second electrode having a second terminal, and a dielectric spacer disposed therebetween. The terminals of the electrodes are exposed at positions outside of the housing so that selected terminal contact wires of the connector make electrical contact with corresponding terminals of the compensation capacitors to provide capacitive coupling between the selected contact wires when the contact wires are engaged by a mating connector. Of note, a design of the type disclosed in the Arnett '742 patent can undesirably decrease contact flexibility, thereby adds complexity to design efforts. In addition, utilizing a curved spring beam contact design can increase unwanted NEXT/FEXT noises because of the adjacencies between pairs.
U.S. Pat. No. 6,443,777 to McCurdy et al. discloses a communication jack having a first and second pairs of contact wires defining corresponding signal paths in the jack. Parallel, co-planar free end portions of the wires are formed to connect electrically with a mating connector that introduces offending crosstalk to the signal paths. First free end portions of the first pair of contact wires are supported adjacent one another, and second free portions of the second pair are supported adjacent corresponding ones of the first free end portions. Intermediate sections of the first pair of contact wires diverge vertically and traverse one another to align adjacent to corresponding intermediate sections of the second pair of wires to produce inductive compensation coupling to counter the offending crosstalk from the plug. Capacitive compensation coupling may be obtained for the contact wires via one or more printed wiring boards supported on or in the jack housing.
Another method for crosstalk noise reduction and control in connecting hardware is addressed in commonly assigned U.S. Pat. No. 5,618,185 to Aekins. A connector for communications systems includes four input terminals and four output terminals in ordered arrays. A circuit electrically couples respective input and output terminals and cancels crosstalk induced across adjacent connector terminals. The circuit includes four conductive paths between the respective input and output terminals. Sections of two adjacent paths are in close proximity and cross each other between the input and output terminal. At least two of the paths have sets of adjacent vias connected in series between the input and output terminals. The subject matter of the Aekins '185 patent is hereby incorporated by reference.
Alternative conductor layouts for purposes of jack/plug combinations have been proposed. For example, U.S. Pat. No. 6,162,077 to Laes et al. and U.S. Pat. No. 6,193,533 to De Win et al. disclose male/female connector designs wherein shielded wire pairs are arranged with a plurality of side-by-side contacts and additional contact pairs positioned at respective corners of the male/female connector housings. The foregoing arrangement of contacts/contact pairs for shielded cables is embodied in an International Standard—IEC 60603-7-7—the contents of which are hereby incorporated herein by reference. The noted IEC standard applies to high speed communication applications with 8 position, pairs in metal foil (PIMF) shielded, free and fixed connectors, for data transmissions with frequencies up to 600 MHz.
Despite efforts to date, a need remains for connector designs that reliably and effectively address the potential for crosstalk noise, e.g., at higher transmission frequencies. In addition, a need remains for connector designs that compensate for crosstalk without adding undue complexity and/or potential cost to the connector design and/or manufacture. Moreover, a need remains for connector designs that accommodate and/or facilitate the introduction or non-introduction of compensation as may be desired based on variable factors encountered in use, e.g., different plug designs and/or plugs having differing contact layouts.
These and other needs are satisfied by the systems and connector designs disclosed herein, as will be apparent from the detailed description which follows, particularly when read in conjunction with the figures appended hereto.